This invention relates to a shutter assembly, and more particularly to a shutter assembly for an automatic gamma counting instrument.
In radioactivity analyzing systems, such as gamma counting systems, the trend has been toward automatic systems wherein a plurality (sometimes 300 or more) radioactive samples traverse a common plane by such means as a link chain conveyor (see U.S. Pat. No. 3,604,935), the conveyor being automatically incremented to place a vial containing a sample in position for lowering into a sample counting chamber. The sample so counted is then elevated and the next sample in sequence is then lowered into the counting chamber. As the number of samples handled by the automatic counting apparatus increase, the probability of the counting chamber receiving spurious signals from the samples not being counted substantially increases.
In beta counting instruments a disc member has often been employed for rotation (see U.S. Pat. No. 3,626,190) about an axis parallel to the counting chamber axis, the disc being of relatively thin construction with an aperture extending therethrough for positioning in alignment with the sample chamber during insertion of a sample and out of alignment with the sample chamber during the measuring cycle. However, such discs are not effective for radioactivity or gamma counting instruments. Ideally, to provide effective shielding to the sample chamber during the counting process in a gamma instrument, solid lead of substantial configuration must be used. With such large lead shutters, problems associated with moving and precisely positioning the lead shutters have been encountered due to the high inertial forces encountered with a large moving mass.